A plebiscite on same-sex marriage is looking less likely, with the Federal Opposition determined to have a parliamentary vote to change marriage laws instead.

Key points:

Chalmers says plebiscite would "waste" $160m

Di Natale says it is already known voters support gay marriage

Hinch says plebiscite would make Australia a "laughing stock"

The Government has promised to have a national vote — or plebiscite — to determine whether same sex marriage should be allowed.

But the Greens, Labor and the three Senators from the Nick Xenophon Team are all firm that a plebiscite is unnecessary.

That would make it impossible for the Government to pass a law to have a national vote.

Labor frontbencher Jim Chalmers has told the ABC a vote in Parliament is the simplest and cheapest way to determine the marriage laws.

"I think it says it all about Malcolm Turnbull's weakness that he is prepared to waste $160 million of taxpayers' money," he said.

"We are trying to get the parliamentary outcome that people expect us to get. We are putting all of our effort into that.

"We don't think it should get to a plebiscite for a whole range of reasons, including the divisive nature of a plebiscite and the waste of money."

'The plebiscite is pointless'

Until now Labor has not explicitly said if it would try to block legislation to set up a plebiscite, but Mr Chalmers said it was his position and that of his colleagues that changing the marriage laws should be done with a simple parliamentary vote instead.

Analysis and opinion

Arriving at Parliament for induction, Senator Skye Kakoschke-Moore said the Nick Xenophon Team's policy was for a free vote in Parliament.

"$160 million is an awful lot of money to spend on a process that at the end of the day won't necessarily be legally binding on the Government," Senator Kakoshcke-Moore said.

Greens leader Richard Di Natale said Parliament could agree to same-sex marriage when it meets for the first time next Tuesday, "but instead, the Liberals want to run a costly and divisive public vote that may be ignored by many of their so-called representatives anyway".

"The plebiscite is pointless," Senator Di Natale said.

"We already know there's overwhelming support for marriage equality in the community and in the parliament so it can't be seen as anything but a delay tactic."

'We will become a laughing stock'

New senator Derryn Hinch is also firmly opposed to a plebiscite.

He told Sky News that the Prime Minister should have held a parliamentary vote to change the marriage laws before calling the election.

"You don't need a plebiscite — they didn't have a plebiscite when John Howard toughened the Marriage Act to put the words man and woman back in there," he said.

"They didn't say we must go to the people. You have been elected by the people — save $160 million."

Senator Hinch compared it to the unsuccessful referendum in 1999 to become a republic.

"They will muddy the question and muddy the waters so much it will get a no vote," he said.

"It could be off the agenda for 20 years and we will become an international laughing stock."